Myocardial necrosis following myocardial ischemia is thought to be aggravated by tachycardia, a circumstance which increases the oxygen requirements of normal heart muscle. However, in dogs with five hours of ischemia, a heart rate increase from 120 to 150 beats per minute did not increase the amount of necrosis, although it decreased ischemic zone blood flow slightly. Moderate tachycardia in myocardial ischemia may not alter myocardial metabolism or coronary blood flow sufficienty to produce deleterious effects.